Manufacturers of cars or trucks having automatic transmissions are required to install a so called park/neutral switch in the vehicle which prevents the operation of the starter motor when the transmission is in driving engagement with the wheels. Typically the switch is connected to the shift linkage of the transmission. When the transmission is shifted in PARK or NEUTRAL the switch allows the engine to be cranked by closing the electric circuit of the starter motor. In any other transmission mode the switch assumes an open condition preventing the starter motor from being energized.
After market remote vehicle starting systems that function by way of radio link are designed to interface with the park/neutral switch in order to determine if the transmission is in a mode allowing the engine to be remotely started in a safe manner. Typically, the slave controller of the starting system which is mounted on board the vehicle observes the state of conduction of the park/neutral switch, upon reception of a radio transmission signalling to start the engine. The slave controller will implement the start engine command only if the park/neutral switch is closed.
However, most cars or trucks having a manual transmission have no factory installed device allowing to determine whether the transmission is in neutral or in gear. In an attempt to overcome this limitation manufacturers of remote vehicle starting systems have developed simple electromechanical switches coupled to the shift linkage of the transmission. This approach is satisfactory when the switch is new. However, the protection it offers against remote starting with the transmission in gear is compromised over time because the switch may eventually malfunction as a result of normal wear or simply lack of proper adjustment. In view of the serious consequences which could result from remote starting of a motor vehicle with the transmission is gear, the industry is presently trying to develop a fail safe device that would positively prevent the engine from starting unless the transmission is, in fact, in the neutral position (or park, if available).